The present invention relates to an electronic component, and more particularly, it relates to a radial lead type electronic component which comprises a plurality of plate-type lead terminals projecting from its protective resin member in the same direction.
FIG. 18 shows a well-known electronic component for automatic insertion, which is mounted on a printed circuit board by an automatic inserter. This electronic component comprises three plate-type lead terminals 100, 101 and 102 of punched metal plates, which are provided with elongated leg portions 100a, 101a and 102a projecting in a common plane from a protective resin member 104 in the same direction. Head portions 100b, 101b and 102b of the lead terminals 100 to 102 are soldered to an element 103, and the protective resin member 104 seals the periphery of the element 103 including the head portions 100b to 102b.
As shown in FIG. 19, wide body portions 100c, 101c and 102c are provided between the leg portions 100a to 102a and the head portions 100b to 102b of the lead terminals 100 to 102. These body portions 100c to 102c are provided on legside ends with inclined edges 100d, 100e, 101d, 101e, 102d and 102e, which define positions for stopping insertion in through holes 106, 107 and 108 of a printed circuit board 105. The inclined edges cause the body portions to gradually taper toward the leg portions, in order to relieve the component from a shock applied upon insertion in the through holes 106 to 108, as well as to bite into upper edges of the through holes 106 to 108 so that the component will be retained on the printed circuit board 105. The inclined edges are bilaterally symmetrical, such that inclinations .theta..sub.17 of the outer inclined edges 100d and 102d of the outer lead terminals 100 and 102, inclinations .theta..sub.18 of the inner inclined edges 100e and 102e thereof and inclinations .theta..sub.19 and .theta..sub.20 of the outer inclined edges 101d and 101e of the central lead terminal 101 are equal to each other, as follows: EQU .theta..sub.17 =.theta..sub.18 =.theta..sub.19 =.theta..sub.20
The above described prior art component is disadvantageous in that portions of the protective resin member 104 between the central lead terminal 101 and the outer lead terminals 100 and 102 are apt to cause cracks 109 as shown in FIG. 18, or may be ruptured when the component is inserted in the printed circuit board by an inserter. Such cracking of the protective resin member 104 leads to defective sealing, breakage of the element 103, defective connection between the element 103 and the lead terminals 100 to 102, and the like.
The cracks 109 or rupture of the protective resin member 104 may occur at the following two stages:
When the element is automatically inserted in the printed circuit board 105, the component body is chucked by an automatic inserter and the leg portions 100a to 102a of the lead terminals 100 to 102 are first inserted in the through holes 106 to 108 of the printed circuit board 105, and then the top surface of the electronic component is driven by a pusher so that the inclined edges bite into the edges of the through holes 106 to 108. First stage cracking occurs at this time. If the pitch centers of the through holes 106 to 108 are completely aligned with those of the lead terminals 100 to 102, the inclined edges 100d, 100e, 102d and 102e of the outer lead terminals 100 and 102 simultaneously strike the upper edges of the through holes 106 and 108, so that reactive forces F.sub.3 and F.sub.4 acting on side edges of the lead terminals 100 and 102 cancel each other and apply no bending stress to the electronic component. In practice, however, the side edges of the outer lead terminals 100 and 102 may not uniformly strike the through holes 106 and 108 due to dimensional errors between the pitches of the through holes 106 to 108 and the lead terminals 100 to 102, chuck error of the automatic inserter, etc., but only the inner inclined edges 100e and 102e of the lead terminals 100 and 102 may strike the upper edges of the through holes 106 and 108. In this case, only the reactive forces F.sub.4 caused by driving of the top surface of the component, acts to externally tear the outer lead terminals 100 and 102. It is to be noted that the protective resin is fairly resistant to a compressive stress while it is extremely weak against a tensile stress. For example, the tensile strength of phenol denatured epoxy resin, which is widely applied to a protective resin member for a piezoelectric component, is merely a little less than 40% of its compressive strength. Therefore the protective resin member 104 is easily cracked when such tearing force F.sub.4 acts on the lead terminals 100 and 102 externally.
Second-stage cracking occurs in a cut-and-clinch operation. After the top surface of the electronic component is driven by the pusher as mentioned above, lower parts of the leg portions coming out through the holes 106 to 108 are shortened by cutting and clinched at one time. The outer lead terminals 100 to 102 are outwardly clinched as shown by two-dot chain lines in FIG. 18, and the central lead terminal 101 is transversely clinched. This cut-and-clinch operation goes on while the top surface of the component is continuously pressed by the pusher. At this time, cut-and-clinch forces F.sub.5 for the outer lead terminals 100 and 102 act in a direction which will increase the reactive forces F.sub.4 caused by pressing the top surface, whereby a larger force acts on the component due to outward pulling on the outer lead terminals 100 and 102. Consequently, the protective resin member 104, which has been almost cracked at the first stage, is completely cracked at this second stage.
The aforementioned problem also takes place in another type of electronic component having terminal configurations shown in FIGS. 20 and 21. In this case, inclined edges 110d, 110e, 112d and 112e of outer lead terminals 110 and 112 are asymmetrical, such that inclinations .theta..sub.22 of the inner inclined edges 110e and 112e are greater than inclinations .theta..sub.21 of the outer inclined edges 110d and 112d. On the other hand, a central lead terminal 111 has symmetrical inclined edges 111d and 111e. The inclinations are set as follows: EQU .theta..sub.21 &lt;.theta..sub.23 =.theta..sub.24 &lt;.theta..sub.22
In this case, reactive forces F.sub.6, which are caused when a top surface of the component is driven by the pusher, regularly act in a direction for outwardly pulling the lead terminals 110 and 112, while cut-and-clinch forces F.sub.7 act to increase the reactive forces F.sub.6. Thus, the rate of occurrence of defects is increased as compared with the component shown in FIG. 18.
It is possible to solve the aforementioned problems by improving the strength of the protective resin member. However, various characteristics are required for the protective resin member. For example, especially in the case of an energy trapped type ceramic resonator, since the process of its production includes cavity-forming as described in U.S. Pat. No. 3,747,176, the protective resin member is possibly required the following two properties besides strength: being able to absorb cavity-forming materials such as wax when heated, casting not too much shrinkage stress on an internal ceramic element when hardened. In practice, it has been extremely difficult to develop a protective resin member which can satisfy all such conditions, due to conflicting requirements therefor. As the result, it has been impossible to exclusively improve the strength of the protective resin member and to prevent the aforementioned defects, and reliability has been thus reduced. The aforementioned problems may be caused not only in an electronic component for automatic insertion, but also in that for manual insertion, i.e., the so-called bulk component, which is not cut and clinched. When the electronic component is pressed on a printed circuit board so that it is attached thereto, the first-stage cracking may occur.